and were used as reservoirs , together with some water ##proof ##ed natural depression ##s . the main plaza ##s were surfaced with stucco and laid at a gradient that channel ##led rainfall into a system of canals that fed the reservoirs . the residential area of ti ##kal covers an estimated 60 square kilometres ( 23 sq mi ) , much of which has not yet been cleared , mapped , or excavated . a huge set of earth ##works discovered by dennis e . pu ##les ##ton and donald call ##end ##er in the 1960s rings ti ##kal with a 6 @ - @ metre ( 20 ft ) wide trench behind a ramp ##art . the 16 square kilometres ( 6 @ . @ 2
and were used as reservoirs, together with some waterproofed natural depressions. the main plazas were surfaced with stucco and laid at a gradient that channelled rainfall into a system of canals that fed the reservoirs. the residential area of tikal covers an estimated 60 square kilometres ( 23 sq mi ), much of which has not yet been cleared, mapped, or excavated. a huge set of earthworks discovered by dennis e. puleston and donald callender in the 1960s rings tikal with a 6 @ - @ metre ( 20 ft ) wide trench behind a rampart. the 16 square kilometres ( 6 @. @ 2